This is not supported by myself or the folks who develop and maintain Mach-II for ColdFusion but I do get a few emails asking about it every year, so here it is.
The API and configuration manual from the old website (tgz).
Note: Don't use PHP 4 plugins with the PHP 5 core files! It might work or you may see some really weird errors like variables disappearing. It didn't seem to be a problem with Mach-II. I've seen it happen with older versions of PHP 5, I don't know if it's been fixed or not.